The quality of images reproduced over a television, a display panel, or by a printing system may be judged with respect to three characteristics: tone scale, image sharpness, and graininess. For digital type of image reproduction devices such as display panels, television monitors, and dot matrix printers there is a direct dependence of these characteristics on the reproduction device system parameters. The tone scale image quality depends on both the system tone reproduction curve which defines a gray scale transformation from the original to the reproduced image, and on the number of levels of gray the system is capable of reproducing. The sharpness factor is directly affected by the x and y resolutions of the reproduction device. Higher resolution devices are generally better at reproducing fine details, thereby yielding sharper images. Finally, graininess refers to those image noises which are usually process related and are not part of the original image.
The role of image processing is to decide whether or not to display or to print at each pixel location one of several size dots such that the reconstructed image closely resembles the original. Jun Okya and Yukie Tokunaga in "Gray Scale Printing on Plain Paper Using Thermal Ink-Transfer Imaging", Journal of Imaging Technology, Vol. 10, No. 2, April 1984, discuss a three level image processing algorithm for image reproduction.
Other known digital image processing algorithms are for binary fixed size print dots or display spots. They all are able to reproduce well some of the image types: text and line drawing, continuous tone images, and halftone pictorials. But they are unable to reproduce well all image types. The present generation of printers and displays poorly mimic the halftone technique of the printing industry because of insufficient dot resolution. Thus it would be advantageous if the printers and displays could overcome these short comings in a system that reproduces high quality images of all types.